1. Field of the Invention
This invention relates to a desensitizing composition and more specifically relates to a desensitizing composition which reduces or eliminates the effect of a color developer (a solid acid) capable of coloring a color former (a substantially colorless electron donating organic compound).
2. Description of the Prior Art
It has long been known to obtain a color image by the reaction of a color former and a color developer. The principle is practically utilized in pressure-sensitive copying sheets (for example, as disclosed in U.S. Pat. Nos. 2,505,470; 2,505,489; 2,550,471; 2,548,366; 2,712,507; 2,730,456; 2,730,457 and 3,418,250) and heat-sensitive recording sheets (for example, as disclosed in Japanese Patent Publication No. 4,160/68 and U.S. Pat. No. 2,939,009). Furthermore, a printing method is also known in which a color image is formed by supplying an ink containing a color former through a medium such as a stencil to a sheet coated with a color developer (for example, as disclosed in German Patent Laid-Open Application No. 1,939,962).
Pressure-sensitive copying sheets can be prepared by dissolving a color former in a solvent such as chlorinated paraffin, alkylnaphthalene, alkylated diphenylethane or alkylated diphenylmethane, dispersing the solution in a binder or incorporating the solution in microcapsules, and then coating the dispersion or microcapsules on a support such as papers or plastic films, on the one hand, and coating on acid clay, a phenol-formaldehyde resin, metal salts of aromatic carboxylic acids, or the like, as a color developer, on the other hand.
Heat-sensitive recording sheets can be prepared by coating a color former and a color developer together with a heat-fusible substance such as acetanilide on a support. A heat-fusible substance is a substance which melts on heating and dissolves the color former.
Generally, a color former and a color developer are coated over the entire surface of the same side or the opposite sides of a support or the surfaces of different supports. Therefore, it is necessary to prevent a color reaction using some method in the portions in which the formation of a color image is not desired or not required. For this purpose, a desensitizing agent is usually coated by printing the desensitizing agent in selected areas on a layer coated with a color developer to prevent a color reaction.
Known desensitizing agents are, for example, high molecular weight primary alkylamines such as dodecylamine and quaternary ammonium salts such as dodecyltrimethylammonium chloride as described in U.S. Pat. No. 2,777,780; tertiary amines such as monoalkylamine-, aralkylamine- or ethanolamineethylene oxide adducts as described in Japanese Patent Publication No. 29,546/71; or secondary alkylamines such as didodecylamine, tertiary alkylamines such as triethylamine, primary arylamines such as aniline or aralkylamines such as benzylamine.
However, conventional desensitizing agents have their respective disadvantages, and it is, therefore, desired to develop better desensitizing agents. For example, most of the conventional desensitizing agents exhibit insufficient desensitizing effects and, particularly, are not equally effective with respect to all types of color developers.
Conventional desensitizing agents which exhibit high desensitizing effects are higly water-soluble and hygroscopic and, when desensitizing compositions are prepared using these desensitizing agents, the desensitizing compositions absorb moisture (particularly, in a high humidity environment) and the binder precipitates. This causes the viscosity of the desensitizing compositions to be insufficient, so that the desensitizing compositions can not be smoothly coated. Also, wavelike wrinkles occur in the surface coated with the desensitizing agent. Moreover, when the desensitizing agent is left together with microcapsules, moisture in the atmosphere which is absorbed in the desensitizing agent causes the membranes of the microcapsules to swell, and as the case may be, even destroys the membranes. As a barely hygroscopic desensitizing agent, an adduct of an amine and propylene oxide is disclosed in Japanese Patent Laid-Open Application No. 6,805/73. However, this desensitizing agent has a disadvantage that the desensitizing effect of this agent is inferior to that of an adduct of an amine and ethylene oxide (as disclosed in Japanese Patent Publication No. 29,546/71) which has been generally used so far. Particularly, the desensitizing effect of the adduct of an amine and propylene oxide is insufficient for color formers of the xanthene series such as 7-diethylamino-3-benzylaminofluoran.